sill.] THE FROG. 173 



are contractile muscular sacs, whicli are connected on the one 

 hand with the lymphatic vessels and on the other with large 

 veins in their neighbourhood ; and which pump the lymph 

 contained in the wide lymphatic vessels and in the pleuro- 

 peritoneal cavity of the Frog, into these veins. 



The anterior lymph-hearts are situated close to the trans- 

 verse processes of the third vertebra, below the edge of the 

 scapula ; the posterior pair lie one on each side of the uro- 

 style, and their pulsations may be observed by carefully watch- 

 ing the integument in this region in a living Frog. 



The Thymus gland is a small rounded body situated 

 immediately behind the suspensorium, in a position corre- 

 sponding to the dorsal ends of the obliterated branchial 

 arches. 



The Thyroid gland appears to be represented by two or 

 more oval bodies, which are found attached to the lingual 

 vessels and between the aortic and pulmo-cutaneous trunks. 



The Adrenal glands are yellow bodies imbedded in the 

 ventral face of the kidney. 



The slit-like glottis of the Frog is foi-med by the apposi- 

 tion of two longitudinal folds of the mucous membrane of the 

 mouth, each of which contains a cartilage of similar form. 

 These cartilages are the arytenoid cartilages. They are 

 articulated with an annular cartilage {laryngo-tracheal) which 

 supports the wall of the very short chamber which represents 

 the larynx and trachea. When the two folds of the glottis 

 are divaricated, there are seen between them two mem- 

 branous pouches, the free edges of which meet in the middle 

 line, while anteriorly and posteriorly they pass into the 

 mucous membrane which lines the faces of the longitudinal 

 folds. These are the vocal ligaments, and the slit between 



